1. Field of the Invention
This invention relates to a method for mounting flexible materials onto a printing cylinder. More particularly, it relates to a method for mounting flexible printing plates in registration on the cylinder.
2. Description of the Prior Art
Flexographic printing plates are resilient relief image plates made of rubber or photopolymer materials which are used to print on a wide variety of substrates. One critical step in the printing process is the accurate positioning of the printing plates onto the printing cylinder. The printing plate must be positioned such that the printing is parallel to the axis of the cylinder, i.e., not skewed. In multicolor printing, the plates for each different color must be aligned so they print in register. Frequently, this positioning is accomplished using pin registration drilling and mounting devices. The printing plate cylinder is typically removed from the printing press, and the plates are mounted to the cylinder using registration holes often in combination with a separate mounting device. However, for some printing presses, such as those typically used to print corrugated containers, the printing cylinders generally are not removed from the press.
A conventional method for mounting flexographic plates for corrugated printing involves the use of a carrier sheet and a mounter proofer unit. One or more plates are mounted onto a large flexible sheet known as the carrier sheet, and attached with adhesive or stickyback tape. The carrier sheet is then placed on the printing cylinder of the press. For multicolor printing, the plates for each successive color are positioned onto their carrier sheets using a mounter/proofer unit with minor. This practice is time intensive, highly dependent on the operator's skills, and potentially fraught with errors and inconsistent results. As the demands for improved registration increase, this method becomes increasingly unsatisfactory.
A major advance in the method of mounting plates for corrugated printing was achieved by the introduction of a single-head drill. With this drill, the printer was able to drill registration holes in both the carrier sheet and the plates. The plates were then mounted on the carrier sheet using mounting pins and stickyback tape. Once the plates were mounted, the pins were removed. Thus the alignment of the plates on the carrier sheet was the same for each color and the need to use the mounter/proofer was eliminated. Both the speed and the accuracy of the mounting process were improved.
Although registration was improved, another source of registration or alignment error occurs when the carrier sheet is attached to a mounting bar. The carrier sheets are placed on the printing cylinder using the mounting bar which secures the sheet to the cylinder at a slot on the cylinder. In the comtgated printing industry, typically mounting bars are substantially T-shaped or J-shaped member. An end of the carrier sheet is aligned and secured to a mounting bar by stitching, gluing, or stapling. Improvements in registration are still impaired by these techniques which are used to attach the carrier sheet to the mounting bar. These techniques are cumbersome particularly when very large plates are being attached to the mounting bar. While gluing, stapling, or stitching the carrier sheet to the mounting bar, it is difficult to prevent shifting or movement of either. Shifting or movement will mis-align the plate on the printing cylinder and can result in misregistration. Further, once attached to the carrier sheet, the mounting bar is no longer reusable.
Thus, it is an object of the present invention to provide an improved method for attaching a carrier sheet to a mounting bar for use on a printing cylinder. The improved method of this invention is easy to use increasing productivity and substantially eliminates registration errors.